Technical Reqest help with SBC cam selection

I have a 327/300 in the refresh stage. The original 461 1.94/1.60 heads were "misplaced" and the replacement 461's are now 2.02/1.60. After the block machine work and piston selection I'm hoping to come in around 10:1 (10:25 at most), with luck it'll be close enough to dial in with appropriate gasket selection.

EDIT -- Items above in red are incorrect. The current 461 heads are 1.94/1.60. CR is 9.76 with .39 quench.

Bolted to the top and sides will be the original cast iron intake and Carter AFB (575CFM) along with 2" rams horn exhaust. Trailing behind will be a stock 1,500(?) stall TC, powerglide and 3.31 diff. Curb weight just shy of 3,800lbs. What I'd like to do is find a cam that will allow for hometown cruising (1,000-4,500) with decent torque, and yes, on pump gas. ;-)

I know I shouldn't make this an L79 motor given the various constraining parameters I just listed. Still, would be nice to tweak as much as possible while also retaining flat tappet hydrolic. If it were just me and my limited current-tech insight deciding I'd probably stick with a stock 929 (300HP) grind for the reason of much better low-end torque. On the other hand, since I have you guys to lean on I figured you might have some ideas on newer grinds (last 30 years) that might be better suited to the situation.

Appreciate any suggestion on cam selection.

 

Default to L79 anytime you can!
At 10.5 comp. your only a half a point short, will be a runner.

 

Thanks for the reply DDDenny!

Yeah, I really like the L79 but given the curb weight and PG w/stock TC I'm afraid it'll be a dog off the light (stop light that is).

 

I agree with Denny. But with the higher CR you are open to more intake and carb options... thus more cam! But with that it snowballs... you need more gear and so on.

 

I've got an original 300 HP 327 in my 63 Impala. Its .060 over with TRW 10.5 forged domed pistons, and a Comp Cam 262 H cam and valve springs along with headers. Its a M21 four speed and a 3.73 rear end with a Holley 670 CFM Street Avenger carburetor.. The idle sounds real bad (in a good way) and it really pulls. I couldn't be any happier with it.

Gary

 

I use the Lunati 435-460 lift cam in almost all of my mild small block Chevies. Tons of torque and works well with a power brake booster.
Used it in my El camino to tow my 70 Chevelle drag car. The car weighed 3500 lbs. plus the trailer and all my gear. Pulled it all over the south with a 2.41 gear with a th350 with no issues.
Still ran mid 8's in the 1/8th mile. Unhooked the trailer one night after some load mouth kid was saying how fast his pickup was.

 

10:1 CR with iron heads may be a little high to run on pump gas without detonation. About 9-9.5 is the generally accepted max with iron heads on pump gas. Also you do not want to lower compression with a thicker head gasket. It will probably make your quench distance too large, (should be .035-.045") making detonation even more likely.

 

The 3.31's are a little light, though were available with the L79, automatics were not.
Keep in mind, GM was looking out for not only themselves (warranty issues) but the average Joe also that may use these cars as daily drivers, which many were.
Many low/medium stall torque converters are being made that should match up to your combination if there is a concern about surging at stops and they are not very expensive.

 

Comp Cams XE268H
Is a great cam I have a similar combination and love it.

 

I'm happy with comp cams 268H. Replacing the powerglide with a 350 would help.
Pete

 

The 350 hp cam is a great choice. But just to throw a little something else into the mix, try considering replacing the power glide with a 350 turbo. It's amazing how much nicer the motor will react, especially pulling all that weight. You'll enjoy the car much more. Would work well over all with your rear gear choice.

 

That is a nice cam, I went with a Lunati Voodoo that is similar in my 355. Idles nice enough, but the cam is audible. 9.75 static CR, 700 Holley DP, M20 Muncie and 3.89 gears. The car weighs 3500 and it pulls strong.

 

COMP XE 252. Real nice torque in the usable street range. Should work well with high-ish gears

 

All good.
The Comp 268 cam is also a sweet cam, reminds me of the 350 hp cam.
Had one in my 350 in my 66 Suburban that had a 350 turbo behind it, great combination.
As I said previous the converter makes all the difference, don't know the numbers but IIRC it was an RV converter the trans guy sourced. I also put an adjustable vac. modulator in it and played around with shift points with the governor. Valve body mods make a difference also but I'm not sure what my trans guy did.

 

I should add that my truck was a 283/powerglide and boy was it a dog.
No matter what you do with the engine the trans swap should be planned in with the build.

 

Any of the cams mentioned would fit the bill. A TH350 also mentioned would be the biggest improvement along with just a little bit of converter, bingo!

 

X2 on the 300 HP cam a very good choice
Had a '67-327 built to 300HP spec in a 60 Impala years ago and it performed flawlessly for good power in all ranges.

 

Much appreciate all the replies! Apologize for the delayed response.

To clarify one of my notes -- I'm hoping that near stock comp height flat-tops will get me to the 10:1-10:25 ballpark while being able to use gasket selection strictly for purpose of setting quench @ .035-.045. When I get chance to visit my friend's machine shop I'll do a proper CC on the heads and measure piston installed height.

As for cams, I'm really liking the suggestions and the relaying of first-hand experiences. From what I understand (given my expected 10:1+ CR) it would be advantageous to choose a cam with the following taken into account:

1. An LSA of 110-114 -- A higher separation will aid in decreasing effective compression (easing likelihood of detonation), broaden torque range and raise idle vacuum. Down side is it will also move the torque band higher.

2. Amount of overlap -- I see the original 151 and 929 cams have huge overlap (114 and 91 respectively) Those seem a lot higher than equivalent modern grinds. The Comp Cams updated N+L79H and N+300HP, while somewhat similar to the originals, have had the overlaps significantly cut back to 56 and 38 respectively. I do know that a larger overlap can help with mid to upper RPM performance but tends to reduce low RPM vacuum and low-end response. It seems something outside of radical should be looked for, maybe the 40-55 range?

Those are the two items it seems would be most important to consider for my situation. Beyond that I'm pretty sure a dual pattern cam is one of the post 60's advancements that can be considered very useful, especially when combined with the exhaust constricted 461's. That being mentioned, I think I may do a little work on the heads even though they're already ***embled with valve job completed. Working around the pretty 3-angle I want to clean up the runners, match ports, pocket port and round this out with a chamber polish.

Back to the cam. What I've been eyeing mirrors many of the recommendations already posted. A few include:
Comp Cams - N+300P, XE262H, XE256H
Lunati - Voodoo 10120701
Crane - H-260-2, H-266-2, Z-262-2
Summit - SUM-1102, SUM-1103

Please advise if I'm going off track with any of my cam ***umptions. ;-)

Now on to the trans suggestions. You guys really have me contemplating the TH350 swap. I already spent a day overhauling the PG but now that I see how easy the swap would be (only "having to" change out the TC, flexplate along with adding a KD cable) I may place the original-to-the-car trans in storage. I see where TH350's can sell pretty cheap and a quick craigslist shows a couple. One is a used 10k street mile unit with 2,500 converter for $300. Another is a freshly rebuilt but unused unit with a new 1,500 stall converter and a new bare main case for $200...but with a catch. Fella selling it said case cracked at the FP upon final ***embly. Not sure how the front pump case lug would break but that's his statement. I'd be happy to complete the swap over of parts and it would allow for inspection of some of what I'm learning could be parts worthy of closer inspection when o-hauling a TH350 (sprag, roller clutch, etc). The case and converter alone make the "broke" TH350 appealing. Still, I know these trans used can sometime go for next to nothing (sometimes not). So I can always defer this swap for a later date until the perfect specimen shows up or I can make a swap (no, not with my PG).

Again, thanks for the opinions offered!

 

LSA on 112 to 116 is for torque and vacuum. Study a cam catalog for a while, especially marine and 4x4 applications, crossed to fuel injection vacuum spec cams on what LSA does.
The Summit/Federal Mogul cam that has 214/224 at .050 .442/.465 falls between the 300hp and 350 hp 327 cams. This cam causes a beat you can dance to, and have good vacuum.
The popular cams that make other noises have 110 degree or tighter LSA spec, that does nothing to help with vacuum and low street RPM reality torque.

 

Thanks for the reply patrick2965!

If I read your post correctly it seems I'm on the correct path and in the ballpark with preliminary selection. Do keep in mind the one hurdle I'm attempting to mitigate by way of cam specs is the 10:1'ish compression on pump gas. Definitely will be a compromise situation given overall constraints but heartily believe I can "do as little harm as possible" with a wise selection.

Fully concur with your statement about "noisy" cams. I recall while doing research the Thumper cams all had LSAs around 107 and sported the corresponding much larger overlaps.

 

Cam is the very last thing to select in any engine build. If this block has never been decked, the deck height is probably 9.025". The stock pistons probably sit at .025" in the hole. You mentioned "NEAR" stock compression height pistons. Stock comp. hgt. is 1.56". Rebuilders pistons are 1.54", leaving the piston .020 " deeper in the hole. (This is to allow the decks to be milled flat, while not raising compression.) If you have the 1.54" C. H. piston you will be .045" in the hole. No way out of that without decking the block.
As I said. Choosing the cam is the last thing to do. Get you short block all sorted out with proper deck height and quench before even thinking about the cam.
My last couple motor builds, for cam selection, I have called custom cam designers. Chris Straub or Mike Jones are two of the best IMHO. Yes, it will cost you a couple hundred more $$$, but you will end up with a sweet running motor.
Sorry! those compression heights are for a 350 not a 327, but the numbers will work similar to illustrate the point.

 

Thanks for the reply jaw22w!

Looks like you're quoting 350 specs. The 327 is 1.675 OEM. I also did mention the pistons were not finalized. My cam query is based on what should be an attainable target of 10:1. The block was very lightly decked and I'm pretty sure we can get close to .020 with piston selection allowing for quench to be easily tuned via standard gasketing.

Letting the cam experts is an option...

 

Yeah, sorry, I had 350 on the brain. Completely glossed over that it was a 327. Haven't done one of those in years. Just hung up on the "Near" wording.
What ever that vehicle is at 3800 pounds, it need a 383 instead of a 327. IMHO.

 

Don't be misled by the very large values for overlap that you see for the 327/300 or 327/350 cams. Those numbers were charted using .006 lifter rise and the Comp Cams might have been done using .050. Somewhere I have numbers for the GM cams checked at .050, but I can't locate it right now.

 

@jaw22w
I'm with you on both accounts. Too many things swimming around in the ol' noggin to keep everything straight. And yes, a stroker is the logical choice unfortunately I want to keep the 461's and original intake which might prove counter productive in that effort. Not like I'm not already dealing with an equivalent situation.

@Fordors
Ah, great info! I completely wasn't remembering that. I'll try and hunt that info down.

@all
Since my earlier wording was somewhat in-artful I wanted to expound -- If memory serves, my understanding is that, aside from installing dished pistons or setting an overly large quench there really isn't much I can do to lower compression when using these heads. This is the basis of me researching the best compromise of cam specs to allow streetability on pump gas.

I had a few numbers given to me yesterday by my machinist and, although he said he's expecting 9.76:1. I plugged those numbers in and come up with 10.43:1. We'll be talking about that later today to see where one of us is in error.

 

My 355 used Speed Pro flat top pistons, heads are aluminum Dart, 64cc and my static CR is about 9.75:1.

 

Appreciate the reply!

That gives me some optimism of a more workable CR. His numbers had us at .000 deck, 63cc +.043 gasket.

Ha! Received an e-mail from my friend/machinist just seconds before submitting this reply which states

This makes cam selection much easier and less of a compromise.

 

Google "Wallace Racing Calculators". There is an excellent compression ratio calculator there. You can plug in your own numbers and play with them all you like. Stops any guessing. Without an accurate calculation of CR, you can't pick a cam.

 

Will only be accurate if the numbers being input are correct.

 

Check out the Melling cam part number MTC 1. Same specs as the Edelbrock Performer cam. Got one in my Suburban with a 350 and 700R4 with a 3.08 axle. Runs great, plenty of power


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